All, And if this is the correct diagnosis, you should be able to use two voltmeters, one between the pin and ground, And the other between the pin and VCC and read voltages on both. Regards, Jim -----Original Message----- From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of Sean Breheny Sent: Monday, April 02, 2007 1:08 PM To: Microcontroller discussion list - Public. Subject: Re: [EE]: Kirchhoff's Voltage Law - violation? Hi Anand, My guess would be that the output was actually acting as a very weak pull-up (perhaps it was set to be open-drain and we are looking at diode leakage) so that when the meter is put between the pin and Vcc, there is no current flow at all through the meter, so it reads 0 volts. When the meter is placed between the pin and ground, the input impedance of the meter draws enough current to cause a 1 V drop across whatever is pulling the pin high. Sean On 4/2/07, Anand Gadiyar wrote: > Hi all, > > I noticed something interesting while playing around with a > GAL16V8 device. I finally figured it out, but it's an interesting > puzzle and I thought it worth sharing. > > Using a voltmeter, the Vcc pin shows 5 volts with respect to GND. > And a output pin at logic high shows 4 volts with respect to GND. The > same pin shows 0 volts with respect to the Vcc pin. The same is > observed when i used a CRO to look at the waveforms. > > Also tried this on a PALCE22V10 device and it behaves similarly. > > See if you can figure it out. I'm pretty sure you guys will throw > more light on the puzzle, else answers in two days. > > Warm regards, > Anand > > __________________________ > Anand Gadiyar > Indian Institute of Science, > Bangalore - 560 012 > __________________________ > -- > http://www.piclist.com PIC/SX FAQ & list archive View/change your > membership options at http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist